1. Field of the Invention
The present invention relates to a rotary filter color camera.
2. Related Background Art
A rotary filter color camera of the prior art is shown in FIGS. 11 and 12.
Referring to FIG. 11, an image pickup element 2 has an image pickup surface 3. Disposed in front of the image pickup surface is a tricolor rotary filter 1 which is rotated at uniform speed by a filter driving system 5. The reference numeral 4 denotes a lead on which a video signal is generated from the image pickup element 2.
In the above-mentioned type of rotary color camera, the tricolor filter is divided into sections for three primary colors respectively. When one of the color filter sections enters the area of the image pickup surface, scanning is carried out only one time for all of the pixels on the image pickup surface. This creates a problem as described hereinafter.
Supposing that a red color filter section is now in front of the image pickup surface and scanning is carried out for all of the pixels passed through the red color filter section, there are produced and stored video signals corresponding to the pixels through the red color filter section. In this phase of operation, it is possible that a portion of the red color filter section may remain in the area of the image pickup surface even after the scanning has been completed. In this case, an extra color signal of the remaining portion of the red color filter section is produced and stored before the next filter section, for example, a green color filter section, comes into the area of the image pickup surface. As the result, the extra color signal of the red filter section is undesirably mixed into the normal video signal output generated during the scanning for the green color filter section now in front of the image pickup surface.
This problem is generally called "color mixing". To minimize the problem of color mixing, various complex geometrical designs have been proposed and used for the prior art rotary color filter. FIG. 12 illustrates an example of a rotary color filter designed according to the prior art.
The rotary color filter 1 shown in FIG. 12 has six color filter sections, namely, R (red), G (green), B (blue), R (red), G (green) and B (blue), and six screen sections designated by 1C.
As readily seen, the rotary color filter 1 is composed of many sections having a very complicated geometrical form.
During the time when one of the color filter sections is in the area of the image pickup surface 3, a non-interlaced scanning of the image pickup surface is carried out one time to read out the stored electric charge resulting from the photo-electrical conversion of an image on the image pickup surface 3. Thus, a video signal is produced on lead 4. In this manner, there are obtained six frame video signals in the sequence of R, G, B, R, G, B during one rotation of the rotary color filter 1.
As described above, the prior art rotary color filter needs to be designed very complicatedly and to be made very precisely. In addition, it needs a timing adjustment means for finely adjusting the timing of scanning of the image pickup surface to the phase of rotation of the rotary filter.
Even when the adjustment of timing is ideally performed, another problem is produced from the particular property of the image pickup element called "afterimage". Due to this afterimage, a remaining signal of a previous frame is mixed into the video signal output now generated. Therefore, the problem of color mixing is unavoidable.
A further problem in the prior art rotary tricolor filter is that of shading resulting from variance of current storage time. Current storage time is the time during which photo-electrically converted charges on the image pickup surface are stored The storage time starts at the entrance of one of the color filter sections in the area of the image pickup surface and continues until scanning of pixels on it. Since the color filter sections have a very complicated geometric form as shown above, the current storage time is variable depending on pixels on the image pickup surface. This variation in current storage time appears on a monitor image display in the form of shading.